Have you ever felt your stomach drop before a big presentation? Does seeing a picture of your favorite food make your stomach growl? Does meeting eyes with that special someone in the hallway give you butterflies? Chances are, just by living your normal life, you are already familiar with the relationship between your gut and the brain.

   The gut-brain link has been closely studied for many years. Deemed the “gut-brain axis” by experts in the field of gastroenterology, it is widely known that the two systems communicate bidirectionally via the central nervous system and enteric nervous system, consisting of the brain and spinal cord, and a mesh-like system of neurons that governs the gastrointestinal system, respectively. The scientific community is now exploring the complexities of this relationship, more specifically the “microbiome-gut-brain axis”, or how the bacteria in your gut controls your mind.

   The area of integrative psychiatry, which combines traditional psychiatric models such as therapy and prescriptions with nutrition, metabolics, and hormones, has already been working to treat the psychiatric implications of gut bacteria imbalance. “We have close to 4 pounds of bacteria in our gut, which is pretty much the size of the human brain, and the gut produces this bacteria which helps us absorb nutrients, it makes nutrients for us, and it protects the gut wall,” said Dr. James Greenblatt, a pioneer in the field of integrative psychiatry and an Assistant Clinical Professor of Psychiatry at Tufts University School of Medicine and Dartmouth College Geisel School of Medicine. Environmental conditions that disrupt this internal system, most commonly long-term use of antibiotics, in turn affects the rest of the body. Sometimes antibiotic use can affect gut bacteria “to a point where you have an overgrowth of yeast… and sometimes the yeast can produce byproducts that can affect behavior,” Greenblatt said. These effects include anything from cravings to mood changes to a variety of psychiatric disorders. “It’s not just one [psychiatric disorder],” continued Greenblatt. “We’ve seen it across depression, anxiety, schizophrenia, so it’s pretty safe to say that we’ve seen implications across all psychiatric disorders,” including learning disabilities such as Obsessive Compulsive Disorder (OCD) and Attention Deficit Disorder (ADD).

   An article by ABC News described a case in in which a teenager with severe OCD reached out to Dr. Greenblatt for treatment. “Mary’s parents had been running around for many years and she’d had a poor response to medicine,” Greenblatt said in the article, “When a patient doesn’t respond, that’s a red flag.” According to the article, Greenblatt was able to “dramatically” reduce her symptoms by using high-powered probiotics to boost good bacteria followed by antibiotics.

   Though this is mostly a new area of study among the scientific community, research to back up this type of treatment is incredibly compelling. A study conducted by McMaster University gastroenterologist Premysl Bercik, MD found that giving antibiotics to BALB/c mice, a type of mouse that is usually shy and timid, dramatically changed the composition of their gut bacteria and consequently changed their behavior to bold and outgoing. As soon as the antibiotic regimen was stopped, the mice returned to their cautious selves and their brain chemistry returned to its normal composition. The American Psychological Association (APA) reported that Bercik also found that infecting mice with a parasite that induced chronic, low grade inflammation of the gut suppressed levels of brain-derived neurotrophic factor (BDNF), a neurochemical that promotes neural connections and an important factor in memory and mood in the hippocampus, and caused the mice to behave more anxiously. According to the APA, “When mice were then treated to a 10-day course of the beneficial microbe Bifidobacterium longum, their behavior normalized, as did their BDNF levels.”

   These types of studies indicate a clear connection between mental health and gut bacteria, so why can’t you reach out to your doctor for a prescription probiotic to treat your depression or OCD? Despite heightened interest in this area of study, there is very little research confirming a clear link between gut bacteria and mental health in humans. “Before probiotics could become an established part of treatment, we would need to learn more about how they might affect the brain, how the effects of different probiotics might differ, how long the effects would last, what dosages would be effective, and whether there would be any risks to such treatment,” said Charlotte Armstrong, a representative of the National Institute of Mental Health (NIMH). Organizations like the NIMH are already supporting research to investigate the relationship between gut bacteria, the brain and mental health in humans to provide information to guide the development of treatments using probiotics. “The punchline is that we have lots of research,” says Dr. Greenblatt, “and what needs to get better fined tuned is the clinical implications.”